Ultra wide angle zoom lens in projection display system

ABSTRACT

An ultra wide angle zoom lens for a projection display system, includes: a liquid crystal panel displaying an image; a first lens group having a positive refractive power, formed by combination of two or more lenses, and correcting chromatic and spherical aberrations of incident light from the liquid crystal panel; and a total reflection mirror reflecting the incident light from the first lens group in a predetermined direction; a second lens group having a negative refractive power, formed by combination of two or more lenses, and correcting distortion and astigmatism of the incident light from the total reflection mirror. Here, a projection lens is constructed so that a magnification of the projection lens is adjusted by movement of the first lens group along an optical axis, and the second lens group is moved forward and backward according to the adjusted magnification of the projection lens so that a lens focusing can be adjusted, thereby satisfying the following equation: 3.2&lt;bf1/f1&lt;3.5; 0.75&lt;f1/f2&lt;1.0; and 5.0&lt;d8/f1&lt;7.0. Here, ‘bf1’ is a rear focal distance, ‘f1’ is a focal distance of the whole lenses, ‘f2’ is a focal distance of the second lens group and ‘d8’ is a distance between the first lens group  70  and the second lens group.

This application claims the benefit of the Korean Application No.P2003-0077971 filed on Nov. 5, 2003, which is hereby incorporated byreference.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a projection optical system, and moreparticularly, to an ultra wide angle zoom lens for a rear projection TV(television), which can be used in all fields irrespective of athickness and display screen size of a TV system.

2. Discussion of the Related Art

Recently, with increase of request for a large-sized screen and ahigh-definition image, projection systems that enlarge and project smallimages using a projection lens have been rapidly spread. The projectionsystems are roughly classified into a front projection system and a rearprojection system depending on a direction of an image projected on ascreen. The rear projection system has received much attention due to anadvantage that a relatively bright image can be displayed even in aplace where surroundings are bright.

A good example of the rear projection system includes a projection TV.In the projection TV, a cathode ray tube (CRT) mode has been mainly usedas a light source for displaying small images. However, the projectionTV of a CRT mode has a limitation in obtaining a small and slim size dueto a size of the CRT. For this reason, it is difficult to display alarge sized screen and obtain luminance required for high resolution inthe projection TV.

To solve such problems, there has been suggested a projection TV basedon a flat display that can obtain a large sized screen at a thinthickness.

Examples of the flat display include a liquid crystal display (LCD), aplasma display panel (PDP), a field emission display (FED), and anelectro-luminescence (EL) device.

Among them, the projection TV based on a LCD projects light emitted froma light source onto the LCD and displays an image of a liquid crystalpanel on a screen by using a projection lens system. Since the image isenlarged and projected on the screen using the liquid crystal panel ofhigh image quality and a small size, a large sized screen image can beeasily obtained and a small and slim sized projection system can beobtained. The projection display system based on a liquid crystal panelcan obtain relatively high resolution and high luminance compared to theCRT. Therefore, it is expected that a large sized screen can bedisplayed.

The projection display system based on a liquid crystal panel includesan optical engine, a total reflection mirror and a screen. The opticalengine includes an illuminating system, a liquid crystal panel and aprojection lens system.

In the projection display system, the illuminating system generateslight and irradiates the generated light onto the liquid crystal panel.The liquid crystal panel displays an image by controlling transmissivityof incident light from the lighting system in accordance with an imagesignal. The projection lens system enlarges and projects the image fromthe liquid crystal panel and displays the image on the screen, therebyenabling a viewer to view the image displayed on the screen 15.

In this case, the image projected by the projection lens system istotally reflected by the total reflection mirror to change a light path.The image reflected by the total reflection mirror moves through thechanged light path to the screen and then is displayed on the screen. Ifthe projected image is directly projected from the rear of the screenwithout any change of the light path by the total reflection mirror, thethickness of the system becomes great. Accordingly, it is desirable tochange the light path using the total reflection mirror so as to reducethe thickness of the system.

FIG. 1 is a schematic diagram illustrating the related art projectiondisplay system based on a liquid display panel.

Referring to FIG. 1, the related art projection display system includesan illuminating system, a liquid crystal panel and a projection lenssystem. The illuminating system includes a light source having anelliptical or parabolic reflection mirror 10 and a lamp 12, and firstand second fly eye lenses (FEL) 22 and 24 and a polarizing beam splitterarray (PBS array) 26 and a condensing lens 28 arranged between the lightsource 20 and a first dichroic mirror 30. The liquid crystal panelincludes dichroic mirrors 30 and 34 and total reflection mirrors 32, 38and 42. The projection lens system includes a dichroic prism 46 and aprojection lens 48. Additionally, the projection display system furtherincludes first and second relay lens 36 and 40, Red/Green/Blue (RGB)liquid crystal panels 44R, 44G and 44B, and a screen 50.

An operation of the projection display system will now be described indetail with reference to FIG. 1.

Referring again to FIG. 1, visible lights emitted from the lamp 12 arereflected by the elliptical or parabolic reflection mirror 10 and thenmoves to the first FEL 22. The first FEL 22 divides incident lights on acell basis and focuses the divided lights upon respective cells of thesecond FEL 24. The second FEL 24 convert incident lights into parallellights to then send the parallel lights to the PBS array 26. The PBSarray 26 splits incident light into linearly polarized lights having thesame axis, namely a P wave and an S-wave, and then converts the P-waveinto an S-wave by a wavelength plate attached partially on its rearsurface.

Accordingly, incident lights are all converted into linearly polarizedlights of one direction, namely S-waves, whereby nearly all the lightsemitted from the light source are inputted to the RGB liquid crystalpanels 44R, 44G and 44B. At this time, the condensing lens 28 condenseslights outputted from the PBS array 26 to the liquid crystal panels 44.

The first and second dichroic mirrors 30 and 34 are arranged between thecondensing lens 28 and the RGB liquid crystal panels 44R, 44G and 44B.

That is, the first total reflection mirror 32 and the red liquid crystalpanel 44R are arranged to one side of the first dichroic mirror 30, andthe second dichroic mirror 34 is arranged to another side of the firstdichroic 30.

The green liquid crystal panel 44G is arranged to one side of the seconddichroic mirror 34, and the first relay lens 36, the second totalreflection mirror 38, the second relay lens 40, the third totalreflection mirror 42 and the blue liquid crystal panel 44B are arrangedto another side of the second dichroic mirror 34.

The dichroic prism 46 is arranged on three surfaces of the RGB liquidcrystal panels 44R, 44G, and 44B, and the projection lens 48 and thescreen 50 are arranged to the remaining side of the dichroic prism 46.

At this time, the total reflection mirror 32 totally reflects red lightfrom the first dichroic mirror 30 to thereby transmit the reflected ared light to the red liquid crystal panel 44R. Here, the red liquidcrystal panel 44R is a transmissive LCD, which transmits the red lighttransmitted by the first total reflection mirror 32 to the dichroicprism 46.

Also, the second dichroic mirror 34 reflects a green light out of thelights having passed through the first dichroic mirror 30 whiletransmitting a blue light out of the lights having passed through thefirst dichroic mirror 30. Accordingly, the green light reflected by thesecond dichroic mirror 34 is transmitted to the green liquid crystalpanel 44G. Here, the green liquid crystal panel 44G is a transmissiveLCD, which transmits the green light transmitted by the second dichroicmirror 34 to the dichroic prism 46.

Also, the blue light having passed through the second dichroic mirror 34is transmitted through the first relay lens 36, the second totalreflection mirror 38, the second relay lens 40 and the third totalreflection mirror 42 to the blue liquid crystal panel 44B. In this case,the first and second relay lenses 36 and 40 are field lenses, whichdelay a focus of the blue light prior to transmission of the blue lightto the blue liquid crystal panel 44B. Here, the blue liquid crystalpanel 44B is a transmissive LCD, which transmits the blue lighttransmitted by the third total reflection mirror 42 to the dichroicprism 46.

In this manner, the RGB liquid crystal panels 44R, 44G and 44Brespectively reproduce a light image of each color by means of thereceived R, G and B lights in accordance to an image signal. In thiscase, an S-wave inputted to each of the RGB liquid crystal panels 44R,44G and 44B is converted into a P-wave by each liquid crystal panel.

In this manner, the dichroic prism 46 combines received red, green andblue lights by using three-color image information from the RGB liquidcrystal panels 44R, 44G and 44B. That is, the dichroic prism 46 reflectsred and blue lights toward the projection lens 48 while transmitting agreen light to the projection lens 48, thereby combining red, green andblue images.

Thereafter, the projection lens 48 enlarges the images from the dichroicprism 46 to then project the enlarged images on the screen 50.

The so-constructed projection display system can be small andlightweight.

Additionally, researches for reducing the thickness of the projectiondisplay system while increasing its screen size, have been conducted. Tomake the size of the screen large and reduce the thickness of thesystem, it is necessary to decrease a projection distance between thescreen 50 and the projection lens 48.

For this, the projection lens system includes a first lens group havinga positive refractive power, and a second lens group having a negativerefractive power. At this time, a total reflection mirror for changingthe light path is disposed between the first lens group and the secondlens group to form an “L” shaped projection lens system, whereby thethickness and the height of the system can be reduced.

However, the “L” shaped projection lens system should make the negativerefractive power of the second lens group great to obtain a shortprojection distance. In this case, aberrations such as distortion, coma,and astigmatism occur greatly.

SUMMARY OF THE INVENTION

Accordingly, the present invention is directed to a projection lenssystem of a projection display system that substantially obviates one ormore problems due to limitations and disadvantages of the related art.

An object of the present invention is to provide a projection lenssystem of a projection display system, which can reproduce a clearpicture while correcting aberrations.

Additional advantages, objects, and features of the invention will beset forth in part in the description which follows and in part willbecome apparent to those having ordinary skill in the art uponexamination of the following or may be learned from practice of theinvention. The objectives and other advantages of the invention may berealized and attained by the structure particularly pointed out in thewritten description and claims hereof as well as the appended drawings.

To achieve these objects and other advantages and in accordance with thepurpose of the invention, as embodied and broadly described herein, anultra wide angel zoom lens for a projection display system, includes: anoptical engine comprising a liquid crystal panel for reproducing lightgenerated by an illuminating system as an image according to an imagesignal; and a projection lens system comprising at least two lenses,enlarging the image transmitted from the optical engine and projectingthe enlarged imaged on a screen by using the lenses, wherein one groupof the lenses adjusts a lens magnification and the other group of thelenses adjusting lens focusing according to the adjusted lensmagnification.

Preferably, a retro ratio (bf1/f1) for determining the size of theprojection lens system installed between the optical engine and thescreen is within 3.2 through 3.5, wherein ‘bf1’ is a rear focal distanceand ‘f1’ is a focal distance of the whole lenses.

Preferably, the projection lens system includes: a first lens grouparranged between the liquid crystal panel and the screen and having atleast two lenses of a positive refractive power; a second lens grouparranged between the first lens group and the screen and having at leasttwo lenses of a negative refractive power; and a first total reflectionmirror arranged between the first lens group and the second lens groupso that an optical axis is ‘L’-shaped.

Preferably, the first lens group includes: a first spherical lenspositioned near the first total reflection mirror and having a positiverefractive power; a non-spherical lens positioned near the firstspherical mirror and having a positive refractive power; a contact lenspositioned near the non-spherical lens, wherein a positive sphericallens contacts with a negative spherical lens in the contact lens; and asecond spherical lens positioned near the contact lens and having apositive refractive power.

Preferably, the second lens group includes: first and second convexlenses arranged near the screen and having a negative refractive power;a non-spherical lens positioned near the first and second convex lenses;and a spherical lens positioned near the non-spherical lens and having apositive refractive power.

Preferably, refractive powers of the first and second lens groups aredetermined so that a focal distance ratio of the first lens group to thesecond lens group is within 0.7 through 1.0.

Preferably, the first lens group and the second lens group are made ofglass or plastics.

Preferably, a ratio (d8/f1) of a distance (d8) between the first totalreflection mirror and the first lens group to a distance (f1) betweenthe first total reflection mirror and the second lens group is within5.0 through 7.0.

In another aspect of the present invention, an ultra wide angle zoomlens in a projection display system, includes: a liquid crystal paneldisplaying an image; a first lens group having a positive refractivepower, formed by combination of two or more lenses, and correctingchromatic and spherical aberrations of incident light from the liquidcrystal panel; and a total reflection mirror reflecting the incidentlight from the first lens group in a predetermined direction; a secondlens group having a negative refractive power, formed by combination oftwo or more lenses, and correcting distortion and astigmatism of theincident light from the total reflection mirror, wherein a projectionlens is constructed so that a magnification of the projection lens isadjusted by movement of the first lens group along an optical axis, andthe second lens group is moved forward and backward according to theadjusted magnification of the projection lens so that a lens focusingcan be adjusted, thereby satisfying the following equation:3.2<bf1/f1<3.5; 0.75<f1/f2<1.0; and 5.0<d8/f1<7.0.

Here, ‘bf1’ is a rear focal distance, ‘f1’ is a focal distance of thewhole lenses, ‘f2’ is a focal distance of the second lens group and ‘d8’is a distance between the first lens group 70 and the second lens group.

Preferably, the first lens group comprises at least one plasticnon-spherical lens having a positive refractive power.

Preferably, the second lens group comprises at least one plasticnon-spherical lens having a negative refractive power.

Preferably, the total reflection mirror reflects an incident light sothat an angel θ between an optical axis of light transmitted from thefirst lens group and an optical axis of light transmitted to the secondlens group is within 30° through 90°.

Preferably, the total reflection mirror is made of glass of plastics.

Preferably, focusing is performed by moving at least one of the firstlens group and the second lens group.

Preferably, focusing is performed by moving a spherical lens included inthe first lens and positioned near the total reflection mirror.

It is to be understood that both the foregoing general description andthe following detailed description of the present invention areexemplary and explanatory and are intended to provide furtherexplanation of the invention as claimed.

BRIEF DESCRIPTION OF THE DRAWINGS

The accompanying drawings, which are included to provide a furtherunderstanding of the invention and are incorporated in and constitute apart of this application, illustrate embodiment(s) of the invention andtogether with the description serve to explain the principle of theinvention. In the drawings:

FIG. 1 is a schematic diagram illustrating the related art projectiondisplay system based on a liquid crystal panel;

FIG. 2 is a schematic diagram illustrating a structure of an ultra wideangle zoom lens for a projection TV according to an embodiment of thepresent invention;

FIG. 3 is a schematic diagram illustrating a projection lens systemaccording to an embodiment of the present invention;

FIGS. 4A, 5A and 6A are graphs illustrating spherical aberrationcharacteristics of the projection lens according to an embodiment of thepresent invention;

FIGS. 4B, 5B and 6B are graphs illustrating image plane curvaturecharacteristics (astigmatic field curves) of the projection lensaccording to an embodiment of the present invention; and

FIGS. 4C, 5C and 6C are graphs illustrating distortion characteristicsof the projection lens according to an embodiment of the presentinvention.

DETAILED DESCRIPTION OF THE INVENTION

Reference will now be made in detail to the preferred embodiments of thepresent invention, examples of which are illustrated in the accompanyingdrawings. Wherever possible, the same reference numbers will be usedthroughout the drawings to refer to the same or like parts.

FIG. 2 is a schematic diagram illustrating a structure of an ultra wideangle zoom lens for a projection TV according to an embodiment of thepresent invention.

Referring to FIG. 2, the ultra wide angle zoom lens includes an opticalengine 52, a projection lens system 54, a second total reflection mirror58 and a screen 60. The optical engine 52 includes a liquid crystalpanel for reproducing lights transmitted from an illuminating system asan image in accordance with an image signal. The projection lens systemincludes a first total reflection mirror 56 and enlarges and projectsthe image from the liquid crystal panel. The second total reflectionmirror 58 moves the light path from the projection lens system 54 to thescreen 60. In other words, the second total reflection mirror 58reflects the light image from the liquid crystal panel to thereby sendthe reflected image to the screen 60. The screen 60 displays the imagefrom the second total reflection mirror 58.

In the optical unit 52, the illuminating system generates lights to thenirradiate the generated lights onto the liquid crystal panel. At thistime, the liquid crystal panel adjusts a transmittance of the lightsfrom the illuminating system in accordance with an image signal tothereby reproduce an image. The projection lens system 54 has a “L”shape by means of the total reflection mirror 56, and enlarges andprojects the image from the liquid crystal panel and then displays theresulting image on the screen 60.

FIG. 3 is a schematic diagram illustrating in detail the projection lenssystem 54 according to an embodiment of the present invention.

Referring to FIG. 3, the projection lens system 54 includes a liquidcrystal panel 61, a first lens group 70 arranged between a prism 100 andthe screen 60 and having a positive refractive power, a second lensgroup 90 arranged between the first lens group 70 and the screen 60 andhaving a negative refractive power, and the total reflection mirror 56.

The first lens group 70 includes a first spherical lens 72 having apositive refractive power, a plastic non-spherical lens 74 having apositive refractive power, a contact lens 77 in which a positivespherical lens 76 contacts with a negative spherical lens 78, and asecond spherical lens 80 having a positive refractive power.

Accordingly, the first lens group 70 has a positive refractive power onthe whole and thereby corrects chromatic aberration and sphericalaberration of incident light from the liquid crystal panel 61.

The total reflection mirror 56 converts an advance path of light havingpassed through the first lens group 70 to thereby cause the light tomove to the second lens group. 90. In other words, the total reflectionmirror 56 reflects the incident light from the first lens group 70toward the second lens group 90 at a predetermined angle. Thepredetermined angle is defined as an angle θ between an optical axis ofthe incident light from the first lens group 70 and an optical axis oflight reflected by the total reflection mirror 56 and transmitted to thesecond lens group 90. Such a predetermined angle is within the range of30°° to 90°. The total reflection mirror 56 is made of glass or plasticmaterial. A reflecting surface of the total reflection mirror 56 has aplane shape or non-spherical surface shape.

The second lens group 90 includes first and second convex lenses 82 and84 having a negative refractive power, a plastic non-spherical lens 86,and a spherical lens 88 having a positive refractive power.

By combination of such lenses, the second lens group 90 has a negativerefractive power as a whole. In the second lens group 90, the first andsecond convex lenses 82 and 84 are in contact with the non-sphericallens 86 at their edges, thereby correcting a distortion and aastigmatism of light emitted from the total reflection mirror 56.

The so-constructed projection lens system 54 is constructed to satisfythe following Equations (1), (2) and (3). $\begin{matrix}{3.2 < \frac{bfl}{fl} < 3.5} & (1) \\{0.75 < {\frac{f1}{f2}} < 1.0} & (2) \\{5.0 < \frac{d8}{f1} < 7.0} & (3)\end{matrix}$

Here, bf1 defined as a back focal length represents a focal distancebetween the liquid crystal panel 61 and the spherical lens 80 of thefirst lens group 70, f1 defined as a focal length represents a focaldistance of the whole lenses, namely the first lens group 70, f2represents a focal distance of the second lens group 90, and d8represents a focal distance between the first lens group 70 and thesecond lens group 90.

The Equation (1) is directed to a ratio of bf1 to f1, i.e., a retroratio, and determines the size that can arrange the projection lenssystem between the liquid crystal panel 61 and the screen 60.

If the retro ratio has a value of 3.5 or greater, the size of theprojection lens system becomes greater. In this case, it is difficult tocorrect an aberration. On the other hand, if the retro ratio has a valueof 3.2 or below, better aberration and optical characteristics can beobtained but it is difficult to form the system. Accordingly, the valueof the retro ratio should satisfy the condition of the equation (1).

The Equation (2) represents a refractive power of the first lens group70 and the second lens group 90 and shows the condition that can correctaberration.

If a ratio of f1 to f2 is greater than 1.0, the refractive power of thesecond lens group 90 becomes weak to thereby facilitate aberrationcorrection. However, the distance between the screen 60 and theprojection lens system 54 becomes longer. In this case, formation of thesystem having a thin size becomes difficult. Also, if a ratio of f1 tof2 is less than 0.7, the refractive power of the second lens group 90becomes intensive so as to facilitate a small size and ultra wideoptical angle of the projection lens system 54. However, a surface R2 ofthe first convex lens 82 in the second lens group 90 becomes close tohemisphere so as to make its production impossible and cause astigmatismand image plane curvature. Therefore, the ratio of f2 to f2 shouldsatisfy the condition of the equation (2).

The Equation (3) represents whether a total reflection mirror can bearranged between the first lens group 70 and the second lens group 90.

In the Equation (3), if a d8 to f1 ratio is less than 5.0, the distancebetween the first and second lens groups 70 and 90 becomes short. Inthis case, it is difficult to arrange the total reflection mirror 56between the first lens group 70 and the second lens group 90. Also, if ad8 to f1 ratio is greater than 7.0, the projection lens system 54becomes longer. In this case, formation of the system having a thin sizebecomes difficult. Accordingly, the d8 to f1 ratio should satisfy thecondition of the equation (3).

Meanwhile, a magnifying power of the projection lens system variesaccording as the first lens group moves in the direction of an opticalaxis. The magnifying power is identical to or below 1.1, and up to65-inch lens can be used without a change in a performance.

If the projection lens system 54 focuses an image on the screen bymoving the whole lens system, the center of the screen 60 is not adaptedto the center of the liquid crystal panel 61. As a result, the imagedeviates from the screen 60. To avoid deviation of the image, a separatedevice is required. In this case, a problem arises in that theproduction cost increases, thereby reducing productivity.

To solve such a problem, the projection lens system 54 of the presentinvention focuses the image on the screen by moving some lenses, therebyimproving definition of the image.

In other words, the image is focused on a focal point on the screen 61by moving the first lens group 70, the spherical lens 72 in the firstlens group 70 or the second lens group 90. Also, a high definition imagecan be obtained without deviating from the screen 60.

The Table 1 below shows factors that can be used for design of theprojection lens system, such as a curvature radius ‘R’ of each lenssurface, the distance (thickness/air interval) ‘t’ between lenssurfaces, and data of refractive index in each lens.

In Table 1, the focal distance is 1.0 to 1.1 mm, a constant ‘Fno’ thatshows brightness of the projection lens is 2.40, and 2ω is 86.0 to89.8°, wherein ‘ω’ represents a picture angle between the projectionlens system and the screen. TABLE 1 Lens Curvature Distance/AirRefractive Surface Radius(R) Interval(t) Index S1 5.02702 0.2440131.63854 S2 3.14234 0.976051 S3 5.65115 0.207863 1.48749 S4 2.566652.56665 S5* 6.31314 0.478988 1.490423 S6* 2.22303 A S7 2.79738 0.3045641.78472 S8 −4.06688 0.144600 1.72342 S9 6.56123 1.071848 S10* −2.222350.360596 1.490423 S11* −1.75771 0.063263 S12 −2.76548 0.144600 1.78472S13 2.13918 0.929959 1.48749 S14 −2.76548 0.045188 S15 6.15635 0.5205601.48749 S16 −8.00904 0.045188 S17 17.62675 0.736557 1.48749 S18 −3.06371B S19 Image Plane 0.0Here, ‘*’ represents a non spherical lens.

Non-spherical surface factors determining non-spherical lens surfacesS5, S6, S10 and S11 shown in Table 1 are defined by the followingEquation (4). $\begin{matrix}{{X(r)} = {\frac{{cr}^{2}}{1 + ( {1 - {{Kc}^{2}r^{2}}} )^{1/2}} + {a_{1} \cdot r^{4}} + {a_{2} \cdot r^{6}} + {a_{3} \cdot r^{8}} + \cdots}} & (4)\end{matrix}$

Here, ‘X(r)’ is a Seg value about a non-spherical surface at a pointhaving a height ‘r’ from an optical axis, ‘c’ is a curvature of a lenssurface at an optical axis, ‘K’ is a conic constant and a1, a2, a3, a4are non-spherical coefficients.

Also, coefficients about shapes of non-spherical lens surfaces are shownin Table 2 below. TABLE 2 Lens surface S5 S6 S10 S11 K 4.385768−1.224032 0.527298 −0.227697 a₁   0.198825E−01   0.257097E−01−0.154300E−01   0.863611E−02 a₂ −0.367529E−02 −0.491804E−02−0.559249E−02 −0.683278E−02 a₃   0.501434E−03   0.488546E−03  0.358626E−01   0.259979E−01 a₄ −0.349963E−04 −0.730355E−04−0.223921E−01 −0.159435E−01

By differently adjusting intervals (thickness/air interval) betweenrespective lens surfaces through movement of Lens surfaces S6 and S18respectively expressed as A and B in Table 1, focal distances of fieldsat a wide angle, middle, and tele points can be expressed as Table 3below. TABLE 3 Focal distance (f) A B Fw 7.092083 3.432255 Fm 6.9983303.422244 Ft 6.755535 3.396386

Here, ‘Fw’ represents a focal distance of a field at a wide angle point,‘Fm’ represents a focal distance of a field at a middle point and ‘Ft’represents a focal distance of a field at a tele point.

FIGS. 4 through 6 are graphs illustrating aberration characteristics ofthe projection lens system at a wide angle, middle, and tele points withreference to Table 3.

FIGS. 4A, 5A and 6A are graphs illustrating spherical aberrationcharacteristics of the projection lens according to an embodiment of thepresent invention. Referring to FIGS. 4A, 5A and 6A, a values of aspherical aberration varies depending on the height of the focusedplane, and the range of spherical aberrations deviating from the focusof the projection lens system is about +0.5 mm through −0.3 mm.

FIGS. 4B, 5B and 6B are graphs illustrating image plane curvaturecharacteristics of the projection lens according to an embodiment of thepresent invention. Referring to FIGS. 4B, 5B and 6B, image planecurvature varies depending on the height of the focused plane, and therange of image plane curvature deviating from the focus of theprojection lens system is about +0.02 mm through −0.05 mm.

FIGS. 4C, 5C and 6C are graphs illustrating distortion characteristicsof the projection lens according to an embodiment of the presentinvention. Referring to FIGS. 4C, 5C and 6C, distortion varies dependingon the height of the focused plane. As the height increases, thedistortion increases. The range of distortion deviating from the focusof the projection lens system is about +0.0 mm through −1.5 mm.

Contrary to the prior art aberration characteristic, the aberrationcharacteristic of the projection lens system according to the presentinvention corrects a spherical aberration, image plane curvature, anddistortion, thereby realizing a high performance of the projection lenssystem.

As described above, the ultra wide angle zoom lens in the projectiondisplay system according to the present invention has the followingadvantages.

First, the present invention defines the size of the projection lenssystem that can be installed between a liquid crystal panel and ascreen, thereby making it possible to correct a spherical aberration,image plane curvature, and astigmatism.

Secondly, the present invention can realize a clear picture by moving alens or a lens group constructing the projection lens system.

Thirdly, the present invention can be adopted in the rear projection TVusing sFPD as a device, facilitate a slimness and lightweight system,and has a magnification-changing function in the projection lens so asto cope with a variation in a screen size.

It will be apparent to those skilled in the art that variousmodifications and variations can be made in the present invention. Thus,it is intended that the present invention covers the modifications andvariations of this invention provided they come within the scope of theappended claims and their equivalents.

1. An ultra wide angel zoom lens for a projection display system,comprising: an optical engine comprising a liquid crystal panel forreproducing light generated by an illuminating system as an imageaccording to an image signal; and a projection lens system comprising atleast two lenses, enlarging the image transmitted from the opticalengine and projecting the enlarged imaged on a screen by using thelenses, wherein one group of the lenses adjusts a lens magnification andthe other group of the lenses adjusting lens focusing according to theadjusted lens magnification.
 2. The ultra wide angel zoom lens of claim1, further comprising a second total reflection mirror for reflectinglight emitted by the projection lens system toward the screen.
 3. Theultra wide angel zoom lens of claim 1, wherein the projection lenssystem changes magnification and focusing of the lenses by moving alongan optical axis of the lenses.
 4. The ultra wide angel zoom lens ofclaim 1, wherein a retro ratio (bf1/f1) for determining the size of theprojection lens system installed between the optical engine and thescreen is within 3.2 through 3.5, wherein ‘bf1’ is a rear focal distanceand ‘f1’ is a focal distance of the whole lenses.
 5. The ultra wideangel zoom lens of claim 1, wherein the projection lens systemcomprises: a first lens group arranged between the liquid crystal paneland the screen and having at least two lenses of a positive refractivepower; a second lens group arranged between the first lens group and thescreen and having at least two lenses of a negative refractive power;and a first total reflection mirror arranged between the first lensgroup and the second lens group so that an optical axis is ‘L’-shaped.6. The ultra wide angel zoom lens of claim 5, wherein the first lensgroup comprises: a first spherical lens positioned near the first totalreflection mirror and having a positive refractive power; anon-spherical lens positioned near the first spherical mirror and havinga positive refractive power; a contact lens positioned near thenon-spherical lens, wherein a positive spherical lens contacts with anegative spherical lens in the contact lens; and a second spherical lenspositioned near the contact lens and having a positive refractive power.7. The ultra wide angel zoom lens of claim 5, wherein the second lensgroup comprises: first and second convex lenses arranged near the screenand having a negative refractive power; a non-spherical lens positionednear the first and second convex lenses; and a spherical lens positionednear the non-spherical lens and having a positive refractive power. 8.The ultra wide angel zoom lens of claim 7, wherein the first and secondconvex lenses and the non-spherical lens are formed in such a way thattheir edges are contacted with one another.
 9. The ultra wide angel zoomlens of claim 5, wherein refractive powers of the first and second lensgroups are determined so that a focal distance ratio of the first lensgroup to the second lens group is within 0.7 through 1.0.
 10. The ultrawide angel zoom lens of claim 5, wherein the first lens group and thesecond lens group are made of glass or plastics.
 11. The ultra wideangel zoom lens of claim 5, wherein the first total reflection mirrorreflects an incident light so that an angel θ between an optical axis oflight transmitted from the first lens group and an optical axis of lighttransmitted to the second lens group is within 30° through 90°.
 12. Theultra wide angel zoom lens of claim 5, wherein a ratio (d8/f1) of adistance (d8) between the first total reflection mirror and the firstlens group to a distance (f1) between the first total reflection mirrorand the second lens group is within 5.0 through 7.0.
 13. The ultra wideangel zoom lens of claim 5, wherein the first total reflection mirror ismade of glass or plastics.
 14. The ultra wide angel zoom lens of claim5, wherein a reflection surface of the first total reflection mirror isplane or non-spherical.
 15. An ultra wide angle zoom lens in aprojection display system, comprising: a liquid crystal panel displayingan image; a first lens group having a positive refractive power, formedby combination of two or more lenses, and correcting chromatic andspherical aberrations of incident light from the liquid crystal panel;and a total reflection mirror reflecting the incident light from thefirst lens group in a predetermined direction; a second lens grouphaving a negative refractive power, formed by combination of two or morelenses, and correcting distortion and astigmatism of the incident lightfrom the total reflection mirror, wherein a projection lens isconstructed so that a magnification of the projection lens is adjustedby movement of the first lens group along an optical axis, and thesecond lens group is moved forward and backward according to theadjusted magnification of the projection lens so that a lens focusingcan be adjusted, thereby satisfying the following equation:3.2<bf1/f1<3.5;0.75<f1/f2<1.0; and5.0<d8/f1<7.0, wherein ‘bf1’ is a rear focal distance, ‘f1’ is a focaldistance of the whole lenses, ‘f2’ is a focal distance of the secondlens group and ‘d8’ is a distance between the first lens group 70 andthe second lens group.
 16. The ultra wide angel zoom lens of claim 15,wherein the first lens group comprises at least one plasticnon-spherical lens having a positive refractive power.
 17. The ultrawide angel zoom lens of claim 15, wherein the second lens groupcomprises at least one plastic non-spherical lens having a negativerefractive power.
 18. The ultra wide angel zoom lens of claim 15,wherein the total reflection mirror reflects an incident light so thatan angel θ between an optical axis of light transmitted from the firstlens group and an optical axis of light transmitted to the second lensgroup is within 30° through 90°.
 19. The ultra wide angel zoom lens ofclaim 15, wherein the total reflection mirror is made of glass ofplastics.
 20. The ultra wide angel zoom lens of claim 15, wherein areflection surface of the total reflection mirror is plane ornon-spherical.
 21. The ultra wide angel zoom lens of claim 15, whereinfocusing is performed by moving at least one of the first lens group andthe second lens group.
 22. The ultra wide angel zoom lens of claim 15,wherein focusing is performed by moving a spherical lens included in thefirst lens and positioned near the total reflection mirror.